1. Field of the Invention
In a class D amplifier for driving highly efficiently speakers in an acoustic apparatus, this invention relates to a class D amplifier equipped with a circuit for generating a deformed triangular wave as a comparison waveform necessary for conducting pulse amplitude modulation of an analog input waveform.
2. Description of the Related Art
The class D amplifier according to the prior art uses a triangular wave as a comparison waveform necessary for conducting pulse amplitude modulation of an analog input waveform and this triangular wave is generated from a rectangular wave by using an integration circuit (refer to JP-A-6-319197).
When the triangular wave is used, however, a modulation ratio is likely to get into saturation when pulse amplitude modulation of an input signal having amplitude exceeding the crest of the triangular wave is conducted. Because the input/output characteristics are linear, a large number of odd-numbered order harmonics develop at a large amplitude output reaching the saturation level and DC components are applied for a long time to the speakers as a load. These drawbacks become more remarkable when a power source voltage of the amplification portion is lower.